For input devices of mobile apparatuses placing more importance on the portability and mobile apparatuses placing more importance on display unit such as displays, an input device with a small input unit on the apparatus is desired.
As a method for reducing the layout space of keys of the input unit on the apparatus, there may be a technical method which allots a plurality of functions to a single input. As a related technique of such method, there is a method which places a joystick for detecting tilt angles of top and bottom as well as right and left directions on the apparatus, and switches characters according to the tilt directions (Patent Document 1).
However, with such method, the tilt directions of the joystick for inputting each character are different from the input method of the mobile apparatuses. Thus, a skill for input is required, and input operations in most cases become complicated. Thus, input errors including operation errors occur frequently.
Further, there is also a method which separates a detecting unit as the above-described input unit from the apparatus main body, and places it independently. As an example of a related technique of that kind, there is a method which performs input actions by wearing the detecting unit on the body (Patent Document 2).
However, it is necessary with such method to prepare the input unit separately from the apparatus, so that the portability thereof becomes poor. Further, it is a troublesome work that the operator needs to wear the detecting unit.
Furthermore, as a method for reducing the space of the input unit for detecting actions to the face of the apparatus, there is a method which performs handwriting character input by detecting digital compressions in the X, Y, and Z axis directions. As a related technique of that kind, there is a method which uses track points, and performs handwriting character input from the digital compression change pattern thereof (Patent Document 3).
However, with such method, there is no transposition of the fingertip that performs input actions. Thus, it is difficult to check the actions, so that input errors may be caused thereby.    Patent Document 1: Japanese Unexamined Patent Publication 2005-258734    Patent Document 2: Japanese Unexamined Patent Publication 2004-537802    Patent Document 3: Japanese Unexamined Patent Publication 2005-301874